Shrouded wind turbine system with yaw control

ABSTRACT

A wind energy systems includes a shroud for each turbine. The shroud is adapted to direct and accelerate wind towards the turbine. A strong adaptable support assembly is provided for securing turbines to a structure. An air glide yaw assembly facilitates rotational movement of the structure allowing the turbines to face oncoming wind. The turbine blades are optimized for use with a shroud.

RELATED APPLICATION

This application is a continuation of U.S. patent application Ser. No.11/845,094, filed Aug. 27, 2007 the entire contents of which areincorporated herein by this reference, which claims the benefit ofpriority of U.S. provisional application No. 60/871,135, filed Dec. 21,2006, the entire contents of which are incorporated herein by thisreference.

FIELD OF THE INVENTION

This invention generally relates to devices for use in producingelectric power from wind energy, and more particularly, to an elevatedshrouded wind turbine adapted for yaw movement facing the wind.

BACKGROUND

Most electricity today is generated by burning fossil fuels andproducing steam which is then used drive a steam turbine that, in turn,drives an electrical generator. Unfortunately, however, the world'ssupply of fossil fuels is large, but finite. Exhaustion of low-costfossil fuels will have significant consequences for energy sources aswell as for the manufacture of plastics and many other things.

More serious are concerns about the emissions that result from fossilfuel burning. Fossil fuels constitute a significant repository of carbonburied deep under the ground. Burning them results in the conversion ofthis carbon to carbon dioxide, which is then released into theatmosphere. This results in an increase in the Earth's levels ofatmospheric carbon dioxide, which enhances the greenhouse effect andcontributes to global warming. Depending upon the particular fossil fueland the method of burning, other emissions may be produced as well.Ozone, SO₂, NO₂ and other gases are often released, as well asparticulate matter. Sulfur and nitrogen oxides contribute to smog andacid rain. Fossil fuels, particularly coal, also contain diluteradioactive material, and burning them in very large quantities releasesthis material into the environment, leading to low but real levels oflocal and global radioactive contamination. Coal also contains traces oftoxic heavy elements such as mercury, arsenic and others. Mercuryvaporized in a power plant's boiler may stay suspended in the atmosphereand circulate around the world.

An alternative source of renewable energy, solar cells, also referred toas photovoltaic cells, use the photovoltaic effect of semiconductors togenerate electricity directly from sunlight. Their use has been ratherlimited because of high manufacturing costs. Disadvantageously, themanufacturing process also consumes considerable fossil fuels, resultingin pollution. Additionally, refined silicon required for thesemiconductors is in short supply, making solar cells relatively costly.Solar electricity currently tends to be more expensive than electricitygenerated by other sources. Furthermore, solar energy is not availableat night, may be unavailable due to weather conditions, and may becompromised during winter months; therefore, a storage or complementarypower system is required for most applications.

Moreover, solar energy is inefficient. Expensive solar cells made fromsingle crystal silicon are currently limited to about 25% efficiencybecause they are most sensitive to infrared light, and radiation in thisregion of the electromagnetic spectrum is relatively low in energy.Polycrystalline solar cells are made by a casting process in whichmolten silicon is poured into a mould and allowed to cool, then slicedinto wafers. This process results in cells that are significantly lessexpensive to produce than single crystal cells, but whose efficiency islimited to less than 20% due to internal resistance at the boundaries ofthe silicon crystals. Amorphous cells are made by depositing silicononto a glass substrate from a reactive gas such as silane (SiH₄). Thistype of solar cell can be applied as a thin film to low cost substratessuch as glass or plastic. Thin film cells have a number of advantages,including easier deposition and assembly, the ability to be deposited oninexpensive substrates, the ease of mass production, and the highsuitability to large applications. Since amorphous silicon cells have nocrystal structure at all, their efficiencies are presently only about10% due to significant internal energy losses.

Another attractive alternative source of renewable energy, wind power,produces electricity from the flow of air over the surface of the earth.Wind rotates a rotor mechanically to an electric generator to produceelectricity. Unlike solar cells, properly located wind turbines cangenerate the energy used in its construction within just months ofoperation. Greenhouse gas emissions and air pollution produced byconstruction of a wind turbine are small and declining. There are noemissions or pollution produced by operation of a wind turbine. Modernwind turbines are almost silent and rotate so slowly (in terms ofrevolutions per minute) that they are rarely a serious hazard to birds.Aesthetic, landscape and heritage issues may be a significant issue forcertain wind farms. However, when appropriate planning procedures arefollowed, these risks are minimal and should be weighed against the needto address the threats posed by climate change and the opinions of thebroader community.

Unfortunately, conventional wind turbines suffer several seriousshortcomings. For example, they rely exclusively on ambient wind speed.Nothing is done to accelerate the wind and thereby attempt to improveefficiency of the turbine. Known prior art wind energy systems do notinclude a shroud.

Another shortcoming is serviceability. Conventional rotors, blades andadjacent components are unreachable from the tower for maintenance.Mechanisms configured to retract the rotor towards a tower, or a yawassembly configured to facilitate rotational movement of the shroud androtor to face oncoming wind.

Yet another shortcoming is the stationary structure supporting thenacelle. While many wind turbines include yaw mechanisms to orient thenacelle into the wind, no prior art wind turbine rotates the structuresupporting the nacelle. Thus the structure is stationary and typicallydesigned with a circular or similar cross section, which exhibitssimilar aerodynamic properties from every angle. Such designs exhibitmarginal aerodynamic performance, making the structure more prone todrag and susceptible to failure than a streamlined structure.

Still another shortcoming of conventional wind turbines is the requiredblade size to drive a particular generator. As conventional windturbines do nothing to augment wind speed, power requirements are met bysizing the rotor. A large generator, of course, requires substantialpower provided by a large rotor to turn. This approach ignores therelationship of wind speed to power, whereby an increased wind speedaugments power output. Disadvantageously, a larger rotor increasesmanufacturing and construction costs, stresses on the support structure,wear and tear on bearings, and maintenance costs.

The invention is directed to overcoming one or more of the problems andsolving one or more of the needs as set forth above.

SUMMARY OF THE INVENTION

To solve one or more of the problems set forth above, in an exemplaryimplementation of the invention a wind energy systems is provided with ashroud for each turbine. The shroud is adapted to direct and acceleratewind towards the turbine.

In one aspect of the invention, an exemplary wind turbine systemincludes a shroud having an entrance, throat and exit, the entrancehaving an entrance diameter, the throat having a throat diameter and theexit having an exit diameter, wherein the entrance diameter is greaterthan throat diameter. A rotor assembly includes a hub and a plurality ofblades attached to the hub. The rotor assembly has a diameter less thanthe throat diameter and is centered at the throat of the shroud. Therotor assembly is configured to convert wind energy into rotarymechanical movement of the rotor assembly. The rotor assembly isoperably coupled to a nacelle, which includes an electric generatorconfigured to produce electric power from rotary mechanical movement. Ina preferred embodiment, the plurality of blades consists of fiveidentical blades equally spaced on the hub seventy two degrees apart.The throat diameter is 2% to 20% larger than the diameter of thediameter of the rotor assembly, allowing rotation and deflection of therotor assembly without contact between the blades and shroud. Thetransition from inlet diameter to throat diameter is smooth and gradual,with a shroud pitch of 15 degrees to 60 degrees. The shroud receiveswind and accelerates the received wind to a throat wind velocity, of1.25 to 2.5 times the entrance wind velocity. A support structuresupports the nacelle, rotor assembly and shroud. Each of the pluralityof blades has a twist of approximately 15° to 25°, with a pitch thatvaries from 1° to 5° near the tip to 15° to 25° near the root, and achord length that tapers about 75% to 33% from the root the tip.

In another aspect of the invention, a horizontal actuator for moving thenacelle is provided. The nacelle is operably coupled to the horizontalactuator and the horizontal actuator is operably coupled to the supportstructure. The horizontal actuator is adapted to controllably move thenacelle from a deployed operational position to a retracted maintenanceposition.

In a further aspect of the invention a yaw system is provided to rotatethe rotor assembly, support structure and nacelle. The support structureis mounted atop the yaw system. The yaw system may include an air glidebearing turntable, a gearbox, a drive gear, and a motor. The motordrives the gear box, which drives the drive gear, which drives theturntable. A central air chamber sandwiched between the air glidebearing turntable and the base is adapted to receive pressurized gaswith a lubricant sufficient to exert an upward force equal to 0.5 to 1.5times a weight of the air glide bearing turntable plus the weightsupported by the air glide bearing turntable. A gasket may be sandwichedbetween the air glide bearing turntable and the base. The gasket is alow friction polytetrafluoroethylene (PTFE)-based gasket.

In yet another aspect of the invention the generator includes a servomotor with a position encoder. The position encoder produces outputsignals corresponding to position of the input shaft. A speedup assemblyhas a speedup input shaft and an output speedup shaft. The outputspeedup shaft is adapted to rotate at about 1,500 rpm when the speedupinput shaft rotates at about 30 to 60 rpm. The output speedup shaft iscoupled to the motor input shaft.

BRIEF DESCRIPTION OF THE DRAWINGS

The foregoing and other aspects, objects, features and advantages of theinvention will become better understood with reference to the followingdescription, appended claims, and accompanying drawings, where:

FIG. 1 is a front plan view of an exemplary wind turbine, without ashroud, adapted for controlled yaw movement according to principles ofthe invention; and

FIG. 2 is a profile view of an exemplary wind turbine, without a shroud,adapted for controlled yaw movement according to principles of theinvention; and

FIG. 2A is an profile view of an exemplary mechanical actuator assemblyadapted for linearly moving the nacelle from an operational use positionto a maintenance position according to principles of the invention; and

FIG. 3 is a top plan view of an exemplary wind turbine, without ashroud, adapted for yaw movement facing the wind according to principlesof the invention; and

FIG. 4 is a top plan view of an exemplary tower yaw assembly adapted foryaw movement according to principles of the invention; and

FIG. 4A is a section view of an exemplary tower yaw assembly adapted foryaw movement according to principles of the invention; and

FIG. 5 is an exploded profile view of an exemplary nacelle assemblyaccording to principles of the invention; and

FIG. 6 is a front plan view of an exemplary wind turbine, with a shroud,adapted for controlled yaw movement according to principles of theinvention; and

FIG. 6A is a profile view of an exemplary wind turbine, with a shroud,adapted for controlled yaw movement according to principles of theinvention; and

FIG. 6B is a profile view of an exemplary shroud with velocity vectorsto conceptually illustrate how the shroud affects wind speed accordingto principles of the invention; and

FIG. 7 is a front plan view of a first exemplary truss support assemblyaccording to principles of the invention; and

FIG. 7A is a profile view of a first exemplary truss support assemblyaccording to principles of the invention; and

FIG. 8 is a front plan view of a second exemplary truss support assemblyaccording to principles of the invention; and

FIG. 8A is a profile view of a second exemplary truss support assemblyaccording to principles of the invention; and

FIG. 9 is a front plan view of a third exemplary truss support assemblyaccording to principles of the invention; and

FIG. 9A is a profile view of a third exemplary truss support assemblyaccording to principles of the invention; and

FIG. 10A is a front plan view of an exemplary concrete support structuresupporting a framework comprising a plurality of wind turbines, eachwith a shroud, wherein the framework is adapted for controlled yawmovement according to principles of the invention; and

FIG. 10B is a side plan view of an exemplary concrete support structuresupporting a framework comprising a plurality of wind turbines, eachwith a shroud, wherein the framework is adapted for controlled yawmovement according to principles of the invention; and

FIG. 11 is a side plan view and section views of an exemplary bladeaccording to principles of the invention; and

FIG. 12A is a top plan view and section views of an exemplary bladeaccording to principles of the invention; and

FIG. 12B is a side plan view and section views of an exemplary bladeaccording to principles of the invention; and

FIG. 12C is a side plan view and section views of an exemplary bladeaccording to principles of the invention.

Those skilled in the art will appreciate that the figures are notintended to be drawn to any particular scale; nor are the figuresintended to illustrate every embodiment of the invention. The inventionis not limited to the exemplary embodiments depicted in the figures orthe shapes, relative sizes, ornamental aspects or proportions shown inthe figures.

DETAILED DESCRIPTION

Referring to the Figures, in which like parts are indicated with thesame reference numerals, various views of exemplary wind turbine systemsand assemblies and components thereof according to principles of theinvention are shown. An exemplary wind turbine system according toprinciples of the invention includes a tower construction, a yaw driveassembly, a shroud, a rotor with rotor blades, a nacelle with a drivetrain and miscellaneous components.

A foundation (not shown in the drawings) anchors the system to theground. In order to guarantee stability, one or more piles and/or a flatfoundation may be used, depending on the consistency of the underlyingground. A flat foundation comprises a large reinforced concrete slabwhich forms the footing of the generator. In a pile foundation,foundation plates (plate foundations) are fixed with piles into theearth. This is particularly necessary in soft subsoil.

A tower construction, exemplary embodiments of which are describedbelow, carries the weight of the supported equipment, such as thesupport frame 120, nacelle 115 and rotor blades 105, while withstandingthe huge static loads caused by the varying power of the wind. The towerconstruction elevates the system to a desired height, e.g., thirty feetor more above ground level. A tower construction of concrete, steel orother building materials may be used. The tower construction may be acontainment structure suitable for housing equipment, a lattice or trussassembly, or other suitable stable form. In the case of concrete, thetower may be constructed on site, which simplifies transport andfitting. Alternatively, pre-cast concrete segments may be shipped andassembled on site.

Referring to FIGS. 1, 2 and 3, front plan, profile and top plan views ofan exemplary wind turbine 110, without a shroud, adapted for controlledyaw movement according to principles of the invention are shown. Asupport structure, e.g., support frame 120, is mounted on a turntable130 of a yaw drive assembly 135, controllably driven by a motor 125. Anacelle 115 and rotor assembly, which comprises a hub 580 and plurality(e.g., five) of rotor blades 105, are supported by the frame 120. Themotor 125 may be manually actuated by a switch and/or automaticallyoperated using a programmable logic controller, microcontroller or othercontrol means, to maintain in a direction facing the wind.

In the exemplary embodiment, the frame 120 is comprised of a frameworkof beams forming a rigid A-shaped support structure. However, theinvention is not limited to such a support frame. Any structure suitablefor supporting the nacelle 115 and rotor assembly on the yaw driveassembly 135 may be utilized and comes within the scope of theinvention. Such structures may, for example, include tubular steel,concrete post and lattice structures.

The rotor assembly, with the help of the rotor blades 105, converts theenergy in the wind into rotary mechanical movement. In an exemplaryimplementation, a five-blade, horizontal axis rotor assembly isutilized. The rotor blades 105 may be comprised of fiber reinforced(e.g., glass, aramid or carbon-fiber reinforced) plastics (GRP, CFRP),aluminum, alloys, combinations thereof, or other suitable material. Theblade profile (airfoil shape) is similar to that of an aircraft wing anduses the same aerodynamic principles to generate lift, which cause therotor to rotate.

The rotor comprises multiple rotor blades 105 attached to a hub 580(FIG. 5). The rotor converts the wind energy into a rotation. In anexemplary embodiment, the rotor has five blades, a horizontal axis, anda diameter of approximately fifteen (15) feet or more. The use of five(5) rotor blades 105 allows for a better distribution of mass thanconventional two (2) or three (3) blade designs, which makes rotationsmoother. A five (5) blade design also allows a smaller diameter, thanconventional two (2) or three (3) blade designs that produce similarforces.

The hub 580 is the center of the rotor assembly to which the rotorblades 105 are attached. The hub 580 directs the energy from the rotorblades 105 on to the generator. If the wind turbine has a gearbox, thehub 580 is connected to the gearbox shaft, converting the energy fromthe wind into rotation energy. If the turbine has a direct drive, thehub 580 passes the energy directly to a ring generator. Each rotor blade115 can be attached to the hub 580 in various ways: either in a fixedposition or with pitch adjustment. A fixed hub 580 is sturdy, reducesthe number of movable components that can fail, and is relatively easyto construct. Pitch adjustment enables manual or remote adjustment ofblade pitch to improve efficiency.

The hub 580 thus locates and captures the five rotor blades 105. The hub580 correctly positions the rotor blades 105 for correct tilt andangular placement. The blades are locked in position using heavy dutymechanical clamps and a locking pin. The locking pin uses two hardenedpins locating in a recess in the rotor blade and further locating in thehub 580 to provide positive locking. The blades can be manually adjustedfor pitch in the hub 580.

In a preferred embodiment, each individual rotor blade 115 can beinfinitely adjusted manually, electromechanically or hydraulically, byturning into or out of the wind. In such an embodiment, the rotor bladesmay be positioned at a pitch angle suitable for generating acceptablelift, such as maximum lift, at a design wind speed (e.g., averageprevailing local wind speed for the location of the turbine).

Alternatively, each individual rotor blade 115 can be adjustedautomatically. Actuators for automated or remote pitch adjustment may beeither hydraulic or electromechanical. In an automated embodiment, acontroller monitors the turbine's power output and/or rotational speed.If the wind is too strong, the rotor blades 105 may be pitched slightlyto reduce lift, so that the rotor continues to generate power at ratedcapacity even at high wind speeds. Otherwise, the system may maintainthe rotor blades at a pitch angle suitable for generating acceptablelift, such as maximum lift, for the design or detected wind speed.

Referring now to FIGS. 2 and 2A, an exemplary horizontal actuatorassembly 205 adapted for linearly moving the nacelle 115 from anoperational use position to a maintenance position 230 according toprinciples of the invention is shown. The nacelle is operably coupled tothe horizontal actuator and the horizontal actuator is operably coupledto the support structure. The horizontal actuator is adapted tocontrollably move the nacelle from a deployed operational position to aretracted maintenance position. Any manual or automatic linear actuatorsuitable for reliably moving the nacelle 115 may be utilized. By way ofexample and not limitation, in an exemplary embodiment, the actuatorassembly 205 includes a hand wheel with a handle 210 operably coupled toa rotatable threaded lead screw 220. The leadscrew is screw specializedfor the purpose of translating rotational to linear motion. Themechanical advantage of a leadscrew is determined by the screw pitch orlead. A higher performing, and more expensive, alternative is a ballscrew comprising a threaded shaft that provides a spiral raceway forball bearings which act as a precision screw. Due to inherently highstatic friction, the lead screw is self-locking (i.e., when stopped, alinear force on the nut will not apply a torque to the screw) thusavoiding backdriving. A threaded flange 215 (e.g., a flange with athreaded nut) coupled to the nacelle 115 by a cradle 225 receives thelead screw 220. The threaded flange 215 threadedly travels along thelength of the lead screw 220 as the lead screw is rotated, therebycausing the cradle 225 to glide in a clamp rail, and consequently causethe nacelle 115 to move linearly and horizontally. The lead screw isrotatably fixed to the support frame 120. Aside from rotational motion,the lead screw 220 does not move relative to the support frame 120. Therange of motion of the nacelle extends from a deployed operationposition to a retracted maintenance position 230. In the maintenanceposition 230, the rotor blades 105 are closest to and accessible fromthe support frame 120. In the deployed position, the rotor blades 105are furthest from the support frame 120. Thus, the nacelle 115 may bedriven from a deployed position to a retracted maintenance position 230by rotating the hand wheel with a handle 210. Other means for controlledhorizontal linear movement of the nacelle, including (without imitation)hydraulic, pneumatic and electromechanical actuators, also come withinthe scope of the invention.

To ensure maximum power output from the generator, a wind turbineaccording to principles of the invention is equipped with a yaw system400, as shown in FIGS. 4 and 4A. The yaw system 400 may also be used tobetter position the rotor assembly and nacelle at a position forservicing. The yaw system 400 allows the rotor assembly, nacelle andsupport frame to rotate (i.e., yaw) to face wind. The exemplary yawsystem 400 comprises an air glide bearing turntable 445, a gearbox 415,a drive gear 405 (e.g., pinion gear) on a bearing 425, and an electricmotor 410 (e.g., a servo motor controlled via a communicatively coupledPLC) as a prime mover, i.e., the ultimate source of all mechanicalmovement in the system. A mechanical or hydraulic braking system may beprovided to prevent drift and lock the turntable securely in positionwhen there is no yaw operation. The yaw system is mounted beneath thesupport frame, and may be mounted atop a tower. The motor 410 drives thegear box 415, which drives the drive gear 405. The drive gear 405meshes, with gear teeth of a bull gear 445 coupled to the circumferenceof the turntable 445. Thus, rotation of the drive gear 405 causesrotation of the turntable 445. The turntable 445 is rotatably supportedatop a yaw assembly support base 430 between a plurality of rollerbearings 440. The roller bearings 440 maintain the turntable 445 inproper radial alignment with the pinion gear 405 and limit upwardmovement of the turntable 445 to prevent separation of the turntable 445from the base 430.

To greatly facilitate rotation, the exemplary yaw system includes an airglide bearing subsystem. The air glide bearing subsystem comprises acentral air chamber 435 sandwiched between the turntable 445 and base430. A gasket 420 is sandwiched between the flanged periphery of theturntable 445 and the base 430. Compressed air with a lubricant may bepumped into the chamber 435 through an inlet port at a pressure (e.g.,about 100 psi) sufficient to exert a substantial upward force, e.g., 0.5to 1.5 the total supported weight, including the weight of theturntable. In a preferred implementation, the upward force is less thanthe supported weight (e.g., sum total weight of the turntable, frame,nacelle and rotor assembly), but is sufficient to offset the supportedweight enough to greatly facilitate rotation without breaking the sealmaintained by the gasket 420 between the turntable 445 and the base 430.In a preferred embodiment, one layer or a plurality (e.g., 2 or more)layers of a polytetrafluoroethylene (PTFE)-based gasket, such as a PTFEtape impregnated with brass or bronze (e.g., Garlock® #426 MultifilBearing Tape), may be utilized, to maintain a high integrity lowfriction seal. The air glide bearing assembly 400 thus floats whilecontrolled motion is supplied via a motor.

In an exemplary embodiment a servo motor with a 2:1 belt reductiondrives a 60:1 dodge worm gear further reduced 18:1. Thus, every 6 turnsof the servo motor provides 11 of rotation of the turntable. At 2,160rpm, the servo motor will rotate the turntable 360° in one minute.

The nacelle 115 holds turbine machinery, as shown in the exemplaryexploded view of FIG. 5. In the exemplary embodiment, an acorn nut 590secures a spinner 110 to a spinner standoff 585. Hex safety bolts 505lock blades 105 to the hub 580. A blade clamp 510 with a retaining pin520 is secured to the hub 580 by a hex safety bolt 515. The hub iscoupled to the input shaft of a speedup assembly 560 (i.e., a gearbox)via a spindle 565 with a retaining pin 525 spindle keeper 570 and headcap screw 575. A bushing 535, head cap screw 530 and nut are provided tocouple the cradle 225 to the speedup assembly 560. A coupling 540 joinsthe keyed output shaft of the speedup assembly 560 to the keyed inputshaft of the turbine assembly 550. The turbine assembly 550 employs anintegral servo motor, position encoder and brake in one completepackage. The integral motor design assures maximum efficiency, whilekeeping the overall footprint sleek and out of the air flow. A head capscrew connects the cradle 225 to the turbine assembly 550. For someembodiments, an asynchronous generator may be used. Other embodimentsmay use a synchronous generator. A grid connection of synchronousgenerator is made via a transformer, due to the fixed rotation behavior.

The speedup assembly 560 takes on the task of matching the rotationspeeds of the slow-moving rotor and the fast-moving generator. By way ofexample, the speedup assembly 560 increases the rotation speed from 30to 60 rpm (which is insufficient for producing electrical energy) to1,500 rpm. The preferred speedup assembly 560 has gears generally inparallel on the input side and a planetary gear stage on the outputside, thereby using fewer rotating components than a conventional systemand reduces mechanical stresses and at the same time increases thetechnical service life of the equipment.

Advantageously, a wind turbine system according to principles of theinvention may utilize conventional commercially available electronicequipment, including a generator, a system for grid in-feed of theelectricity, and various sensors and controls. The system for feedingelectricity into the grid depends upon the generator used. In a variablespeed turbine embodiment with a synchronous generator, alternatingcurrent generated fluctuates constantly in frequency and quantity. Inorder for the electricity to be fed into the grid, it is converted intodirect current using a rectifier, filtered and then converted back intoalternating current using an inverter. Voltage is converted forconnection to the level of the grid using a transformer. Sensors formonitoring and control may be provided on and in the nacelle 115 tomeasure wind speed and wind direction, speed of the rotors and thegenerator, the ambient temperature and temperature of individualcomponents, oil pressure, pitch and azimuth angle (yaw mechanism basedon the wind direction) and electrical values, as well as vibrations orvibrations in the nacelle 115. Data from sensor signals may be used tocontrol operation. For example, in response to signals corresponding towind direction, the yaw mechanism may be activated. An exemplary windturbine system according to principles of the invention may also containcomponents lighting, cooling, heating, lightning protection, liftinggear (e.g. winches for spare parts), communications equipment and fireextinguishing equipment.

The nacelle may optionally include temperature control features. Thetemperatures inside a nacelle 115 can be quite high due to the wasteheat from the speedup assembly and the generator. Cooling elements suchas heat sinks, fans and vents may therefore be installed in the nacelle115 to help keep it cool. Heaters may also be provided to warm up theoil in the gearbox in cold climates. Rotor blades 105 may be heated incold climate conditions to prevent them from icing over. Anemometers andweather vanes may also be heated in cold regions to prevent them frommalfunctioning.

Referring now to FIGS. 6 and 6A, front plan and profile views of anexemplary wind turbine, with a shroud, adapted for controlled yawmovement according to principles of the invention are shown. The shroud600 comprises a forward entrance-defining portion 605, a center throatportion 610 and a rear exit-defining portion 615, with the innersurfaces of all three portions defining a circular passageway, and witheach section differing in radius. Thus, the shroud comprises anaxisymmetric tubular structure, converging to a minimum radius in themiddle, making somewhat of an hourglass-shape, with a smooth bell shapedventuri inlet, a circular throat, and a flared exit. The diameter of theinlet, d_(i), is larger than the throat diameter, d_(t). The diameter ofthe exit, d_(e), is also larger than the throat diameter, d_(t), butequal to or less than the diameter of the inlet, d_(i). The diameter ofthe throat 610 of the shroud, d_(t), is slightly larger (e.g., 2% to 20%larger) than the diameter of the rotor assembly with the blades, therebyenabling the rotor with blades to be positioned in or nearby (e.g., ator slightly aft of) the throat section and allowing blade rotation anddeflection without scraping or otherwise contacting the interior surfaceof the shroud. By way of example and not limitation, for a rotor withblades having a diameter of 15 feet, the shroud may feature a throatdiameter, d_(t), of about 17 feet, an inlet diameter, d_(i), of about 25feet, and an exit diameter, d_(e), of about 20 feet. In general, thelarger the ratio of inlet diameter to throat diameter, i.e.,d_(i)/d_(t), the greater the increase in wind speed.

To provide a smooth transition from ambient wind speed V_(i) to throatwind speed V_(t), the transition from inlet diameter, d_(i), to throatdiameter, d_(t), should be smooth and gradual. Discontinuities andsudden changes in diameter facilitate early transition from laminar toundesired turbulent flow. Turbulent flow, is dominated by recirculation,eddies, unsteady vortices, increased drag due to increased boundarylayer skin friction, and chaos, including low momentum diffusion, highmomentum convection, and rapid variation of pressure and velocity inspace and time. Thus turbulence compromises wind speed at the throat,V_(t), and decreases overall system performance and efficiency.

To militate against the onset of turbulence, in an exemplary embodiment,the transition from inlet diameter, d_(i), to throat diameter, d_(t),occurs over a minimum shroud inlet length, l_(i), equal to about 25% to75% of the difference between inlet diameter, d_(i), and throatdiameter, d_(t). Thus, the minimum length increases as the differencebetween the inlet diameter, d_(i), and throat diameter, d_(t) increases.In a particular exemplary embodiment, for a shroud tapering from a 25foot inlet diameter, d_(i), to a 17 foot throat diameter, d_(t), aminimum shroud inlet length, l_(i), equal to about 50% of the differencebetween inlet diameter, d_(i), and throat diameter, d_(t), i.e., 4 feetwhich is 50% of 8 feet, is preferred. In such an exemplary embodiment, atransition length l_(i) of 4 feet or greater (e.g., 4.75 feet) may beused. This gradual tapering results in an acute shroud pitch, α,preferably less than 60°.

In addition, the transition to and from the throat diameter d.sub.t issmooth, gradual and curvaceous. Illustratively, the throat may feature acurved section having a radius, r_(t), of approximately 25% to 65% ofthe total shroud length, l_(i)+l_(e), and a center of curvature in linewith the throat, as shown in FIG. 6A. In a particular exemplaryembodiment, for a shroud with a total length of approximately 7 feet, aradius of curvature, r_(t), for the throat section of approximately 2feet may be provided.

Likewise, the transition from throat diameter, d_(t), to exit diameter,d_(e), should be gradual to avoid low speed transition from laminar toundesired turbulent flow dominated by recirculation, eddies and unsteadyvortices. Such flow, characterized by swirling and reverse current, canoffset the benefit of the accelerated incoming flow and decrease overallsystem performance and efficiency. In an exemplary embodiment, thetransition from throat diameter, d_(t), to exit diameter, d_(e), occursover a minimum shroud exit length, l_(e), equal to about 25% to 85% ofthe difference between exit diameter, d_(e), and throat diameter, d_(t).Thus, the minimum length increases as the difference between the exitdiameter, d_(e), and throat diameter, d_(t) increases. In a particularexemplary embodiment, for a shroud expanding from a 17 foot throatdiameter, d_(t), to a 20 foot exit diameter, d_(e), a minimum shroudexit length, l_(e), equal to about 75% of the difference between exitdiameter, d_(i), and throat diameter, d_(t), i.e., 2.25 feet which is50% of 8 feet, may be used.

The shroud 600 accelerates the flow of air passing through it. The speedof air increases as it moves from the wide entrance through theconverging portion leading to the narrow throat. At or near the throat,the air velocity reaches a maximum. As the shroud cross sectional areagradually diverges from the narrow throat to the wider exit, the airexpands, decelerates and exits.

FIG. 6B is a profile view of an exemplary shroud with velocity vectorsto conceptually illustrate how the shroud affects wind speed accordingto principles of the invention. As discussed above, the shroud amplifiesor increases velocity of wind driving the rotor blades. Wind flowapproaches the shroud at a velocity V_(i). As the wind travels throughthe entrance of the shroud and approaches the throat, it is compressedand accelerates to V_(t). The wind velocity at the throat, V_(t), isgreater than the entrance velocity V_(i), by a factor x, which isgreater than 1.0 (e.g., 1.25 to 2.5). In a particular exemplaryembodiment, x is approximately 2, meaning that wind velocity at thethroat, V_(t), is about twice the entrance velocity V_(i). As wind poweris cubically related to wind speed, a two-fold increase in wind velocityresults in an eight-fold increase in energy output. Rotor blades locatedat or near the throat of the shroud will be subject to the higher windvelocity, thus increasing the rotational speed of the rotor. The gradualtransition or expansion of air passing out to the atmosphere serves toavoid turbulence and reduce aerodynamic losses.

Referring now to FIGS. 7, 7A, 8, 8A and 9 various optional exemplarytruss support tower assemblies according to principles of the inventionare conceptually shown. The assemblies comprise a lattice framework ofcrisscrossed support members and surrounding beams. Each truss supporttower assembly includes one or more elevating sections 710, 810, 920 andone or more elevated sections 705, 805, 905-915 configured to supportone or more rotors, shrouds 600 and nacelles. The entire truss supporttower assembly may be mounted atop and configured for yaw motion on ayaw assembly, such as the yaw assembly described above. Alternatively,each elevated section may be mounted atop and configured for yaw motionon a yaw assembly.

Of course, other support towers may be utilized. As one example, aconcrete tower assembly 1000 featuring a concrete tower, such as a 60feet tall 15 feet diameter concrete tower 1005, as shown in FIG. 10, maybe provided to elevate the system to a desired height, e.g., thirty feetor more above ground level. The tower 1005 may be a containmentstructure suitable for housing equipment. The tower 1005 may beconstructed on site, which simplifies transport and fitting.Alternatively, pre-cast concrete segments may be shipped and assembledon site. An entrance door 1015 is provided in the exemplary embodiment,to allow access to the interior by personnel and equipment. The one ormore wind turbine systems 1020, including a yaw assembly 1010, may besupported on the roof of the tower construction 1005. Access to the roofmay be provided through a suitable opening such as a doorway, trap door,ladder or other access means.

Referring now to FIG. 11, a side plan view and section views of anexemplary, scalable blade 1100 according to principles of the inventionare shown. The blade is not limited to the dimensions or proportionsshown. The mounting shaft 1105 is received by the hub of the rotor. Thecross section profiles (views AA at 19.50 inches from the end of themounting shaft, BB at 36.38 inches from the end of the mounting shaft,CC at 52.25 inches from the end of the mounting shaft, DD at 68.12inches from the end of the mounting shaft and EE at 85.03 inches fromthe end of the mounting shaft) are designed to give low drag and goodlift. The pitch of the cross section profiles varies from 2° near thetip (as in view EE) to 20° near the root (as in view AA), providing anoverall twist of about 18°. In an exemplary embodiment a twist ofapproximately 15° to 25° is preferred. The twist, results in a change inthe true angle of attack for the airfoil that depends on the radiallocation, allowing more pitch at the blade root for easier startup, andless pitch at the tip for better high-speed performance. The length ofthe chord, c, changes (i.e., tapers) about of about 75% to 33% along thelength of the blade, from a maximum near the root (i.e., section AAhaving a chord of about 19.85 inches) to a minimum near the tip (i.e.,section EE having a chord of about 12 inches). The airfoil shaped blade,with a rounded leading edge and sharp trailing edge, twist ofapproximately 15° to 25° produces lift when placed in a wind stream, andtaper of about 60%. By way of example and not limitation, a blade mayhave a twist of approximately 15° to 25°, with a pitch that varies from1° to 5° near the tip to 15° to 25° near the root, and a chord lengththat tapers about 75% to 33% from the root the tip.

Referring now to FIGS. 12A and 12B, top and side plan views of theuncovered spar 1200 over which a skin is formed to create a blade areshown. The spar comprises a thick leading edge stringer 1205 thatterminates at the root with a mounting shaft 1105. A plurality of ribs1215, an angled root stringer 1225 and a wing tip 1230 join a thintrailing edge stringer 1220 to the leading edge stringer 1205.

The spar is filled with foam and a skin is formed over the foam filledstructure to form the blade 1200, as shown in the top plan view of FIG.12C. The skin is preferably a fiber reinforced (e.g., glass, aramid orcarbon-fiber reinforced) plastic. The spar is preferably aluminum or analuminum alloy.

Preferably, wind turbines are positioned to face into the prevailingwind. In some applications, a wind turbine according to principles ofthe invention may use a non-rotatable, fixed base, where prevailingwinds consistently blow from the same direction.

While an exemplary embodiment of the invention has been described, itshould be apparent that modifications and variations thereto arepossible, all of which fall within the true spirit and scope of theinvention. With respect to the above description then, it is to berealized that the optimum relationships for the components and steps ofthe invention, including variations in order, form, content, functionand manner of operation, are deemed readily apparent and obvious to oneskilled in the art, and all equivalent relationships to thoseillustrated in the drawings and described in the specification areintended to be encompassed by the present invention. The abovedescription and drawings are illustrative of modifications that can bemade without departing from the present invention, the scope of which isto be limited only by the following claims. Therefore, the foregoing isconsidered as illustrative only of the principles of the invention.Further, since numerous modifications and changes will readily occur tothose skilled in the art, it is not desired to limit the invention tothe exact construction and operation shown and described, andaccordingly, all suitable modifications and equivalents are intended tofall within the scope of the invention as claimed.

1. A wind turbine system comprising: a shroud having an entrance portionconfigured to receive a fluid flow into the shroud, an exit portionconfigured to exhaust the fluid flow from the shroud, and a throatportion operatively coupling the entrance portion with the exit portion;a rotor assembly comprising a hub and a plurality of blades operativelycoupled with the hub, the plurality of blades being positioned relativeto the shroud to convert energy of the fluid flow into the shroud intorotary mechanical movement of the rotor assembly; an electric generatorassembly operatively coupled with the rotor assembly and configured toconvert the rotary mechanical movement of the rotor assembly intoelectric energy; and, a sensor configured to generate a signalrepresentative of a speed of at least one of the rotor assembly or theelectric generator.
 2. The wind turbine system according to claim 1,wherein the sensor comprises a position encoder.
 3. The wind turbinesystem according to claim 2, wherein: the generator comprises a servomotor having a motor input shaft; and, the position encoder isconfigured to produce output signals corresponding to a position of theinput shaft.
 4. The wind turbine system according to claim 1, furthercomprising: a controller configured to adjust an operational parameterof the rotor assembly in accordance with the signal.
 5. The wind turbinesystem according to claim 4, wherein the controller is configured toadjust a pitch of the plurality of blades relative to the hub inaccordance with the signal.
 6. The wind turbine system according toclaim 5, wherein the entrance portion of the shroud has an entrancediameter, the throat portion has a throat diameter and the exit portionhas an exit diameter, wherein the entrance diameter is greater thanthroat diameter.
 7. The wind turbine system according to claim 6,wherein the throat diameter is 2% to 20% larger than the diameter of thediameter of the rotor assembly, allowing rotation and deflection of therotor assembly without contact between the blades and shroud.
 8. Thewind turbine system according to claim 6, the transition from inletdiameter to throat diameter being smooth and gradual and the pitch ofthe shroud being 15 degrees to 60 degrees.
 9. The wind turbine systemaccording to claim 6, the shroud being adapted to receive wind having anentrance wind velocity and accelerate the received wind to a throat windvelocity, the throat wind velocity being 1.25 to 2.5 times the entrancewind velocity.
 10. The wind turbine system according to claim 1, furthercomprising: a support structure; and a horizontal actuator operablycoupled between the support structure and a nacelle housing the rotorassembly and the electric generator assembly, said horizontal actuatorbeing adapted to controllably move the nacelle relative to the supportstructure from a deployed operational position to a retractedmaintenance position.
 11. The wind turbine system according to claim 1,further comprising: a support structure; a nacelle operably coupled withthe support structure and configured to house the electric generatorassembly; and a yaw system adapted to rotate the rotor assembly, supportstructure and nacelle.
 12. The wind turbine system according to claim 1,further comprising: a support structure; a nacelle operably coupled withthe support structure and configured to house the electric generatorassembly; and a yaw system adapted to rotate the rotor assembly, supportstructure and nacelle, said support structure being mounted atop saidyaw system.
 13. The wind turbine system according to claim 12, whereinthe yaw system comprises an air glide bearing turntable.
 14. The windturbine system according to claim 13, wherein the yaw system comprises agearbox, a drive gear, and a motor, said motor driving the gear box,which drives the drive gear, which drives the turntable.
 15. The windturbine system according to claim 14, wherein the yaw system comprises acentral air chamber sandwiched between the air glide bearing turntableand the base, and adapted to receive pressurized gas sufficient to exertan upward force equal to 0.5 to 1.5 times a weight of the air glidebearing turntable plus a weight supported by the air glide bearingturntable.
 16. The wind turbine system according to claim 15, whereinthe yaw system comprises a gasket sandwiched between the air glidebearing turntable and the base.
 17. The wind turbine system according toclaim 16, wherein: the central air chamber is configured to receivecompressed air with a dispersed lubricant; and, the gasket is apolytetrafluoroethylene (PTFE)-based gasket.
 18. The wind turbine systemaccording to claim 1, said generator comprising a servo motor with aposition encoder.
 19. The wind turbine system according to claim 1, saidgenerator comprising a servo motor having a motor input shaft, and aposition encoder adapted to produce an output signal corresponding toposition of the input shaft, and the system comprising a speedupassembly with a speedup input shaft and an output speedup shaft, saidoutput speedup shaft being adapted to rotate at about 1,500 rpm whensaid speedup input shaft rotates at about 30 to 60 rpm, and said outputspeedup shaft being coupled with the motor input shaft.
 20. The windturbine system according to claim 1, wherein each of said plurality ofblades has a twist of approximately 15° to 25°, with a pitch that variesfrom 1° to 5° near the tip to 15° to 25° near the root, and a chordlength that tapers about 75% to 33% from the root the tip.